The present invention relates to ink jet recording materials (recording materials for ink jet printing), particularly to ink jet recording materials excellent in ink drying property and glossiness.
Ink-jet printing ranks with electrophotography (PPC) as one of the most popular recording processes. Various kinds of top-coated materials for ink-jet printing have been proposed to obtain an image of high quality. As the top-coating for image receiving, a resin having both good water resistance and ink absorbency is generally used as borne on a substrate such as a paper sheet or a film. There have been proposed materials using a graft-polymer or a block polymer (Japanese Patent Application laid-open Publication No. 61-21780), materials using a polyvinyl pyrrolidone and an acrylic acid polymer (Japanese Patent Application laid-open Publication No. 62-218181) and materials used for both ink-jet printing and PPC (Japanese Patent Application laid-open Publication No. 5-177921).
In most of the conventional ink jet recording materials, inorganic pigments such as clay, talc, silica, alumina (aluminum oxide) and titanium oxide are added to the coating in order to improve the ink absorbency of the material. The inorganic pigments are selected considering their transparency or color (transparent or white).
For example, when transparency of the ink jet recording material is required for the application to CHP etc., a transparent crystalline pigment such as alumina or the like is selected. When the ink jet printing material should be white, a white pigment such as talc, titanium oxide or the like is selected.
When the inorganic pigment is selected, consideration should be given not only to the color of the inorganic pigment but also to the dispersability in a coating solution, its effect on the fluidity of the coating solution, and its effects on ink absorbency or drying property of the ink-receiving layer. However, each of the aforementioned inorganic pigments has different characteristics and does not satisfy all of the requirements.
Therefore, an object of the present invention is to provide an ink jet recording material excellent in all of the characteristics such as drying property, ink absorbency, water resistance and the like. Another object of the present invention is to provide an ink jet recording material capable of providing an image of a high quality.
In order to attain the aforementioned objects, the inventors conducted research on inorganic pigments used for the ink-receiving layer of the ink jet recording material and, as the result, found that silica particles surface-doped with alumina (alumina-doped silica) have both characteristics of silica and those of alumina and that their properties are superior to the two inorganic pigments individually or in mixture.
The ink jet recording material according to the present invention has an ink-receiving layer comprising hydrophilic resin and inorganic pigment, wherein the ink-receiving layer contains silica particles surface-doped with alumina as the inorganic pigment. The amount of the alumina is preferably 0.00001 to 20 wt %.
The alumina-doped silica exhibits good fluidity and good dispersability when it is dispersed in a coating solution, and enables formation of a strong coating layer. The ink-receiving layer containing the alumina-doped silica has high water resistance and excellent ink absorbency and is capable of producing an image of high quality.
The amount of the alumina-doped silica is not particularly limited but is preferably 5-200 parts by weight based on 100 parts by weight of the resin.
According to one preferable embodiment of the present invention, the ink receiving layer is formed on a substrate. As the substrate, plastic film and paper sheet are typical.
When a paper sheet is employed, the ink receiving layer may be formed thereon by coating. Alternatively, the paper itself can be the ink receiving layer. In the latter case, the alumina-doped silica can be added to pulps as a loading material for inner sizing or added to a sizing coating as a pigment thereof in a paper manufacturing process.